/Engine/Source/Editor/UMGEditor/Public/WidgetBlueprintEditor.h
Adds external widget whose lifetime should be managed by this editor
void AddExternalEditorWidget ( [FName](API\Runtime\Core\UObject\FName) ID, [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SWidget](API\Runtime\SlateCore\Widgets\SWidget) > InExternalWidget )